Conventional cellular systems typically use a Broadcast Channel (BCH) to communicate information to a mobile user specific to the Radio Access Network (RAN) as well as to a given cell, even before a connection is established. In a TDD system, the BCH is transmitted on the Primary Common Control Physical Channel (PCCPCH). Another example of common channels transmitted on CPCH timeslots is the Forward Access Channel (FACH) which, in TDD, is transmitted on the Secondary Common Control Physical Channel (SCCPCH). As disclosed herein, the term “CPCH timeslot” refers to any timeslot that is used to transmit the CPCH.
Certain reserved timeslots are typically used throughout a subsystem of the TDD system to transmit the CPCH. The subsystem is an ensemble of TDD cells that can interfere with each other because of their relative close proximity, from a path loss point of view, to one another. For example, a subsystem could consist of one floor of a building deployed using multiple cells if the walls of the building would not provide sufficient isolation (from a path loss point of view) to prevent interference from one cell to another. Similarly, an entire building could be considered a subsystem if the floors and ceilings of the building would not provide sufficient isolation (from a path loss point of view) to prevent interference between floors. In an outdoor deployment, a subsystem can be anything from a small district consisting of a few cells to a large metropolitan area.
Depending on the performance of the receivers of the TDD system as well as the radio frequency (RF) isolation between cells, the TDD system may limit the number of timeslots required to transmit the CPCH to one CPCH timeslot. Alternatively, the TDD system may have to use more than one timeslot to ensure good quality on the CPCH (e.g., BCH reception if it is the PCCPCH, FACH block error rate (BLER) if it is the SCCPCH, etc.).
FIG. 1 illustrates the case when more than one timeslot is used in a conventional wireless communication system. Each base station (BS) A-F of the system would use only one of the timeslots 1, 2, 3 for its own CPCH transmission while refraining from transmitting anything on the other timeslots that the system uses for CPCH. Neighboring base stations would use the other timeslots for their CPCH transmissions. A given CPCH timeslot would be used only by base stations that are a certain distance apart from each other, thus enhancing the signal-to-interference ratio (SIR) of the CPCH for the mobile units served by these base stations and ensure contiguous coverage of CPCH. However, this diminishes the system capacity since less time timeslots are available for traffic in Dedicated Physical Channels (DPCHs).
There exists a need for a method and system which selectively reuses some of the CPCH timeslots in a TDD system for transmitting user data.